The present invention relates generally to micro-machined sensors.
Truly low-cost inertial sensors have been a goal of the industry for many years. Until recently, the high cost of precision inertial sensors has precluded their use in automotive applications, consumer electronics, robotics, and a wide range of military applications.
The present invention features a micro-machined angle measurement gyroscope.
In one implementation, the gyroscope includes a substrate; a proof mass coupled to the substrate by an isotropic suspension such that the proof mass can move in any direction in the plane of the substrate; a plurality of drive electrodes configured to cause the proof mass to oscillate in the plane of the substrate; and a plurality of sense electrodes configured to sense the motion of the proof mass in the plane of the substrate.
According to one aspect, each drive electrode moves the proof mass along drive axis, and at least two of the drive axes are mutually orthogonal.
According to one aspect, each sense electrode senses the motion of the proof mass along a sense axis, and at least two of the sense axes are mutually orthogonal.
According to one aspect, the proof mass includes a rigid ring.
According to one aspect, the proof-mass includes one or more concentric rings.
According to one aspect, the substrate has an anchor at the center of the ring, and the ring is connected to the anchor by a one or more flexures.
According to one aspect, each electrode includes an inner electrode located inside the ring and an outer electrode located outside the ring.
According to one aspect, each electrode includes a plurality of comb teeth; the proof mass includes a plurality of comb teeth; and the comb teeth of the electrodes and the proof mass are adjacent.
According to one aspect, the suspension includes a ring attached between the proof mass and the substrate.
According to one aspect, the substrate has an anchor at the center of the ring, and the suspension includes one or more flexures connected between the ring and the anchor.
According to one aspect, the suspension includes a plurality of concentric rings attached between the proof mass and the substrate.
According to one aspect, the gyroscope includes one or more central drive electrode located near the center of the ring.
According to one aspect, the proof mass, electrodes, suspension and substrate are micro-machined from a single crystal of material. The material can be silicon.
In another implementation, the gyroscope includes a substrate; a proof mass suspended above the substrate by an isotropic suspension such that the proof mass can move in any direction in an oscillation plane normal to the substrate; a plurality of drive electrodes configured to cause the proof mass to oscillate in the oscillation plane; and a plurality of sense electrodes configured to sense the motion of the proof mass in the oscillation plane.
According to one aspect, each drive electrode moves the proof mass along a drive axis, and the drive axes of a pair of the drive electrodes are mutually orthogonal.
According to one aspect, each sense electrode senses the motion of the proof mass along a sense axis, and the sense axes of a pair of the sense electrodes are mutually orthogonal.
According to one aspect, each electrode includes a plurality of comb teeth; the proof mass includes a plurality of comb teeth; and the comb teeth of the electrodes and the proof mass are adjacent.
According to one aspect, the suspension includes one or more suspension units each having a flexible beam disposed between the proof mass and an anchor attached to the substrate.
According to one aspect, each suspension unit includes a flexible frame attached between the beam and anchor; a suspension tuning electrode attached to the frame; and an anchored electrode attached to the substrate. A bias voltage between the suspension tuning electrode and the anchored electrode imposes a bias force on the beam.
According to one aspect, the proof mass, electrodes, suspension and substrate are micro-machined from a single block of material. The material can be silicon.
According to one aspect, the gyroscope includes one or more tuning electrodes configured to adjust the frequency of oscillation of the proof-mass.
Advantages that can be seen in implementations of the invention include one or more of the following. A class of monolithic micro-electro-mechanical sensors capable of measuring an angle of object rotation is described. Implementations of x-, y-, and z-axis gyroscopes of this class are described in detail. This novel class of inertial instruments provides accurate information about an object""s rotation in the form of a signal that is proportional to the angle, thus eliminating the necessity for integration of the output signal. In contrast, existing micro-electro-mechanical sensors generally provide a signal proportional to the angular rate; consequently, a numerical or electronic integration of the rate is required in order to obtain the desirable outputxe2x80x94the angle. In general, integration is undesirable because it accumulates errors.
The disclosed approach sharply deviates from the commonly accepted concept that an angle measuring gyroscopes should be a shell. In fact, implementation of an uniform shell on micro-scale is not currently feasible due to limitations of micro-fabrication technologies and small signal-to-noise ratio.The sense area is limited by the shell""s area, so the signal is significantly smaller compare to the signal noise). In the disclosed approach, an xe2x80x9canisotropic lumped mass-spring systemxe2x80x9d is used instead. This approach permits the implementation of an angle gyroscope using micro-electro-mechanical systems (MEMS) technology. According to this approach, an arbitrary shaped proof-mass suspended on a uniform (isotropic) suspension. This permits a significant increase in sense capacitance, and thus achieves a large signal-to-noise ratio.
Further features and advantages of the present invention as well as the structure and operation of various implementations of the present invention are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit of a reference number identifies the drawing in which the reference number first appears.